This invention relates to coating film transfer tools for transferring a coating film onto a receiving surface. The coating film may be an opaque correction film for masking errors in typewritten matter, drawings and the like. Alternatively, the coating film may be an adhesive, a decorative coating, or other material that is to be transferred onto a surface as a coating.
A typical conventional coating film transfer tool comprises a casing into which are built two shafts, one for rotatably supporting a supply reel, and the other for rotatably supporting a take-up reel. A transfer head projects from the casing, and a transfer tape, consisting of a tape base material coated with a coating film, is wound on the supply reel. The base material extends over the transfer head to the take-up reel, and, at the location of the transfer head, the coating film may be transferred from the tape base material to a receiving surface, under pressure applied to the tape by the transfer head. As the transfer operation takes place, the tape is fed from the supply reel, and the base material which remains after the transfer of the coating film takes place at the transfer head, is wound onto the take-up reel.
A drive mechanism, for effecting cooperative rotation of the reels, typically comprises a rubber belt extending over pulleys formed on both reels.
The drive mechanism effects cooperative rotation of the reels such that, in the absence of slippage, the length of the tape base material to be wound onto the take-up reel would exceed the length of the tape fed by the supply reel. Since the length of the tape base material to be wound onto the take-up reel is always greater than the length of tape to be fed from the supply reel, the tape is, at least in theory, prevented from slackening. However, a large tension would be applied to the tape base material in the absence of slippage. Excessive tension on the tape base material is avoided by providing for slippage between elements of the drive mechanism.
The torque in the drive mechanism while slippage is taking place is referred to as xe2x80x9cslipping torquexe2x80x9d. The magnitude of the slipping torque tends to vary periodically as a result of contact conditions between reel support shafts and the reels, deformation of various mechanical parts, variations in manufacturing tolerances, and other causes. If the slipping torque falls below a certain level, the take-up reel can no longer wind the tape base material during a film transfer operation, and the tape base material will begin to slacken. The value of the slipping torque at which this phenomenon occurs is called the xe2x80x9cwinding thresholdxe2x80x9d.
The term xe2x80x9cslipping ratioxe2x80x9d as used herein refers to the ratio of the excess length of tape base material demanded by the take-up reel in the absence of slippage to the length of base material fed from the supply reel. The slipping ratio, of course, changes as the diameters of the wound tape material on the reels change. In the initial stage of operation, when most of the tape base material is wound on the supply reel, and little, if any, is wound on the take-up reel, the slipping ratio tends to be at its lowest level. The slipping ratio increases, as tape is fed from the supply reel to the take-up reel.
Failures in the winding of the tape base material onto the take-up reel tend to occur especially in the initial stages of operation of the tool, when the slipping ratio is relatively low and the cycles of the periodic variations in slipping torque are relatively long.
To prevent the transfer tape base material from slackening while the transfer tool is in use, various measures have been adopted in the past. One such measure is to set the mean value of the slipping torque at a relatively high level so that, even though the slipping torque varies, its value always exceeds the winding threshold. An alternative is to keep the variation of the slipping torque as small as possible, so that it is always above the winding threshold, by improving manufacturing tolerances and precision of assembly.
In the case in which the mean value of the slipping torque is set at a high level, a relatively large force is required to feed the transfer tape from the supply reel in the later stages of operation, when the outer diameter of the transfer tape on the supply reel becomes relatively small. In the case in which measures are taken in manufacture to minimize variation of the slipping torque, parts having high accuracy are required, and lubricants or special materials are needed, and consequently manufacturing costs are increased.
An important object of this invention is to provide an improved coating film transfer tool, which reliably avoids slackening. Another object is to reduce the force required to operate the tool in the later stages of its useful life, when most of the tape base material is wound onto the take-up reel. Still another object is to reduce manufacturing costs.
To address the aforementioned objectives, the invention utilizes a drive mechanism designed to have an initial slipping ratio of 34% or more. More particularly, the coating film transfer tool in accordance with the invention comprising a supply reel, a take-up reel, a transfer head, and a transfer tape comprising a base material and a coating film on the base material. The base material of the tape is wound on the supply reel and extends from the supply reel, over the transfer head, to the take-up reel. The tool further comprises a drive mechanism connected to the supply and take-up reels for causing the take-up reel to rotate in a direction to take up base material fed over the transfer head as the supply reel rotates in a direction to feed tape toward the transfer head. The drive mechanism allows a limited amount of slippage between the supply and take up reels so that, as the tape is unwound from the supply reel, the tape base material is wound onto the take-up reel without being stretched excessively. However, the slipping ratio of the drive mechanism at an initial stage of winding, when a maximum amount of the length of the transfer base material is wound on the supply reel, is at least 34%.
Because of the high initial slipping ratio, the periods of variation in the slipping torque can be made short, and thus the time intervals during which the slipping torque is below the winding threshold are also relatively short. As a result, the transfer tape base material can be prevented from slackening without encountering the problem of excessive force in the latter stages of operation, and without taking special measures in the manufacturing process to minimize the magnitude of slipping torque variations.
Other objects, details and advantages of the invention will be apparent from the following detailed description when read in conjunction with the drawings.